This would be useful for computer support, where a user says, 'When I press x, this number changes and then changes back to what it was before'. This sort of thing is hard to see in a screen grab, but would be easy to see if they could send you a small movie.

Or you could use it to send a friend a small movie of some cool graphics or a game you've got.

So the utility is like the 'Print Scrn' button, but you press a button to start recording, then press again to stop a bit later. It creates a movie file, maybe giving you compression options.